Air metered shock absorber for airplane landing gears



Jan. 25, 1938. R. P. WILLIAMS 2,106,198

AIR METERED SHOCK ABSRBER FOR AIRPLANE LANDING GERS Filed sept. 26, 1954 F/6v./. ef/6.2.

Patented Jan. 25, 1938 l I g UNITED STATES PATENT OFFICE AIR METERED SHOCK ABSORBER FOR AIRPLANE LANDING GEARS Randolph P. Williams, Hampton, Va. Application September 26, 1934, Serial No. '145,809 10 Claims. (Cl. 267-64) (Granted under the act of March 3. 1883, as amended April 30, 1928; 370 0. G. 75'!) The invention described herein may be manuwill be appreciated from the following description factured and used by or for the Government for of a specific embodiment thereof when read in governmental purposes, without the payment t connection with the accompanying drawing, me of any royalty thereon. wherein:

This invention relates generally to vehicle Figure 1 is a view partly in elevation and partly 5 shock-absorbingdevices and more particularly to in section of a shock-absorber embodying the inshock-absorbers of the return oleo type used with vention and shown in the fully extended position.

airplane landing gear to secure resiliency in land- Figure 2 is a similar view of the shock-absorber ing and taxiing. but showing same in apartly compressedl condilo Thev oleo shock absorber in its simplest form tion. l0 consists of a cylinder, lled with a shock-absorb- The' invention, as herein disclosed, consists ing medium such as oil, and a piston having a mainly of a large cylinder I, a smaller cylinder leak orifice of some kind in it through which the or compressed air chamber 3, a free piston `5, a oil is driven when the piston is forced into the smaller hollow piston consisting of a piston head l5 cylinder. The amount of shock absorbed de- 1 and a hollow-piston rod 9, two ribs or oil` l5 pends upon the size of the leak orice and the metering devices II, and the necessary filling length of the stroke. The oleo mechanism itself caps, packing, and plugs. ,The small cylinder 3 affords no means for returning the piston to the is formed integrally with the larger cylinder I extended position after the absorber has been but exteriorly of the latter in the manner shown. compressed and, hence, furnishes no shock-ab- Both cylinders are in communication with each sorbing action to take care ofthe small bumps other through a bottom orifice I3. The large in taining. It iS Customary, therefore. t0 empiston 5 is a oating piston and is inserted in the ploy some sort of an auxiliary device, such as cylinder I for limited travel within the bottom rubber, steel springs, or compressed air, in conportion of the cylinder, an abutment or -stop l5 g 2,. junction with the oleo gear to furnish `the prOper at the bottom .of the cylinder limiting the downcushion for taxiing and to return the gear to its ward travel of the floating piston and preventing extended position after the shock is absorbed. same from completly .covering the orice I3. The chief maintenance on the return type oleo The upper limitv of the piston travel is determined gear is due to the auxiliary taxiing device. Rubby the length of the two ribs I I which extend lonber requires frequent replecinawhile compressed gitudinally of the inner wall of the cylinder in o() air requires an elaborate peeking gland lwhich advance of the floating piston and in overhanggives much trouble. Steel Springs are Het Partieing relation with respect to the latter, as indicated ularly satisfactory and are quite heavy. at l1.

With the OI'egOing in mind. it iS an Object 0f The cylinder space or chamberA I9 above the 3f the present invention to provide an oleo shockfloating piston is filled with a shock-absorbing 35' absorber of such generally improved construction medium, preferably an oil, which is introduced and design as tp Operate With @highly elicierlt into the oil chamber through a filling opening 2l dissipation of energy and without the disadvanin the screw cap 23 at the top of the cylinder. tages mentioned. The smaller cylinder 3 is filled partly with oil Another object of the invention is to provide and partly with air under pressure, both being 40 an oleo shock absorber in which an elastic meintroduced into the cylinderat ,the upper end dium is employed, in conjunction with the shockof the latter, the former through a filling openabsorbing oil of the oleo cylinder, to carry the ing 25 and the latter through an air valve 21. weight of the plane and to absorb the loads inci- The filling openings are provided with, suitable dent to landing and taxiing. closure plugs 29. The smaller cylinder thus con- 45 A further object is to provide a shock-absorber tains an elastic fluid medium and a non-comof the type described in which an initial pressure pressible liquid, the latter also filling the space is controlled by air-metering and in which a con-v below the iioating piston but being prevented trolled pressure is maintained during the comfrom mingling with the oil in the oil chamber I9 pression 0f the deViCe the COUSIUCQR being byreason of the tight sliding t of the oating 50 such as to give a readily calculable operating piston which is so constructed as to prevent the pressure early in the oleo stroke and to maintain passage of air or liquid through vor around it. Va maximum pressure without exceeding the alvThe `pressure exerted by the elastic medium is lowable load factors. transmitted by the liquid of the air chamber 3 other objects and advantages of the invention and the floating piston 5 to the body of oil in u the oil chamber I9, through which it is exerted against the head1 of the hol1ow;piston. 'I'he pressure thus exerted on the hollow piston, 1-9, at the very beginning of the stroke bears a defl- 5 nite relation to the air pressure in the cylinder 3. Hence, the maximum allowable load factors can be utilized almost from the start of the piston stroke, thus ensuring an efcient dissipation'if energy. T his initial pressure is controlled by l air metering, which can be calculated by known physical laws.

The cylinders of the shock-absorber are, connected with a wheel or other movable part of an airplane landing gear by means of a strut 30 xed l to and depending from a bracket 33 which is provided with an internally threaded socket into which the lower end of the cylinder is screwed. The piston head 1 of the hollow piston is secured to the lower end of the hollow piston rod 9 and is positioned at the outer or upper end of the oil chamber I9 ln the fully extended condition of the shockvabsorber. 'Ihe piston rod is adapted to be attached, at its outer end, to the airplane structure and slides in a suitable bearing in the top cap A23 of the oil chamber. When the weight of the airplane comes upon the hollow piston, 19, in landing, the latter is forced inwardly of the chamber I9 and in order that the initial shock of landing may be opposed by a maximum 3Q resistance without exceeding the allowable load factors, means are providedy for controlling the pressure maintained during the piston stroke. 'I'his is accomplished by preventing the ilow of any oil past the piston head 1 until the pressure within the device is built up to the maximum allow'able load factors of the structure. `'I'his occurs in the early part of the piston stroke and is governed by the design of diametrlcally opposed metering ribs "carried by the cylinder wall and 40 operating in grooves, ports, or leak orices 35 arranged at the vedge of the piston head 1 for coaction with the metering ribs, the construction being such as to provide for a metered flow of liquid from beneath the piston head 1, through the orifices 35, into an annular chamber 36 deiined between the hollow piston and cylinder;` there being openings or ports 33 in the hollow piston adjacent the'piston head to permit the flow of liquid-from the'annular chamber into the hollow, -piston rod 9, as the piston and cylinder collapse. These ribs II project from the wall of chamber I3 and are of varying cross sections to vary the effective flow areas 'of the leak oriiices; the upper portions 31 of the ribs being, however, of constant cross section fand engaging in and iilling the piston grooves or ports 35 for a predetermined part oi the piston stroke so that little or no oil passes, the piston head 1 until the latter is at the point A, at which place the cross sectional dimensions of the ribs decrease abruptly to allow the oil to pass through the ports 35. y The cross sectional dimensions of the ribs increase gradually and progressively below the point "A as the ribs approach the bottom of the oil chamber until the cross sectional dimensions at the extreme lower ends I1 are equal to the cross sectional dimensions oi' the upper end portions 31. Consequently, the effective ilow areas of the leak oriilces 35 of the hollow piston, 1 9, are gradually decreased during the -lower part of the piston stroke to maintain uniformity or pressure on the hollow piston. ,f

During flight,.the shock absorber is extended with the floating piston 5 and the hollow piston,

1-9, relatively positioned as shown in Figure 1. Upon landing, the hollow piston, 1-9, moves down in cylinder I and since little or no oil passes the piston head 1, due to the construction of the metering ribs, the floating piston 5 also moves down, forcing oil through the orifice I3 into vthe cylinder 3 and increasing the air and liquid pressure by virtue of the air compression in the cushion chamber 3. Volumes and piston travel are so related as to give from the4 known laws of in physics the desired pressure in the liquid at the moment the contours of the metering ribs change to allow liquid to flow past the piston head 1. Thereafter, during the stroke variation of the ribs, depth increases the efiiciency of the device in l5 dissipating the energy due to fall of the airplane.

'I'hc air column in the compressed air chamber provides, in addition to the above, an elastic medium for absorbing shocks when the airplane is run over the ground; the loads incident to taxi- 2n ing being taken by oscillation of the piston 5 and corresponding oscillations of air pressure in cylinder 3. It thus serves the double purpose of providing an air metering device whereby the liquid pressure on the piston is controlled, and, 25 in addition, enabling the shocks Oilanding and taxiing to be met and absorbed without excessive strain on the airplane structure.

This device gives a readily calculable operating pressure early in the oleo stroke anda highly 30 eiiicient dissipation of energy by virtue of the controlled pressure maintained during the piston stroke.A It will be noted, also, that no metallic springs, rubber, or elaborate packing glands are required in the construction of the absorber and 35 that the design and organization of the parts is such as to give maximum accessibility.

The apparatus described is but one of many possible combinations of cylinders and pistons by which the similar results may be obtained. 40

Having thus described the invention,v what is claimed as new is:-

1. A shock absorber having, in combination, a cylinder, an elastic medium in the cylinder, a piston'mvable inwardly of the cylinder for com- 45 pressing the elastic medium, a mobile non-compressible liquid normally conned between the piston and the elastic medium, and means operating at a predetermined compression of the elastic medium to by-pass the liquid to the outer 50,

cylinder, a piston movable inwardly of the cylin- 55 der-for compressing the elastic medium, a mobile non-compressible 'liquid normally confined between the piston and the elastic medium, and means operating at a predetermined compression of the elastic medium to bypass the liquid to the 60 outer side of the piston during continued inward travel of the. piston and at a rate to maintain a maximum` pressure without exceeding allowable load factors.

3. A shock absorber having, in combination, a 65 cylinder containing a volume of elastic ilent medium under pressure, a piston movable inwardly of the cylinder, a mobile volume of noncompressible liquid within vthe cylinder and normally coniined between the piston and the elastic 70 medium, said elastic medium being compressed] by the movement of the pistoni and liquid in-. wardly of the cylinderfand means operating at a predetermined compression of the elastic medium and at a predetermined portion ot the in- 75 ward travel of the piston to bypass the liquid to the outer side of the piston at a rate to maintain a maximum pressure without exceeding allowable load factors, volumes and piston travel being so related as to give the desired pressure in the liquid at the moment the bypass means allows the liquid to flow to the outer side of the piston.

4. A shock absorber 1 comprising, a cylinder containing a non-compressible liquid and an elastic medium, a floating piston between and separating the liquid and the elastic medium, a load bearing piston in said` cylinder adapted when forced inwardly to move the liquid and floating piston against the elastic medium to compress the same, said load bearing piston having leak orifices, and metering devices in said cylinder normally obstructing the leak orifices at the beginning of the piston stroke and for a predetermined part of the stroke to prevent flow of liquid past the load bearing piston at such time.

v5. A shock absorber comprising relatively large and small cylinders having a communicating orifice, a body of non-compressible liquid in the large cylinder, a body of non-compressible liquid and a volume of elastic fluid in the small cylinder, a floating seal between and separating the contents of the respective cylinders, a piston in the large cylinder and movable against the body of non-compressible liquid, said piston having grooves to permit passage of the said liquid past the said piston, and metering ribsv projecting from the wall of the large cylinder and engaging the said grooves to vary the effective flow areas thereof, said ribs having upper portions of constant cross section engaging in and fully closing the grooves for a predetermined part of the piston stroke and then abruptly decreasing in cross section to entirely clear the grooves and subsequently varying in cross section to maintain uniformity of pressure on the piston during the remainder of its stroke.

6. A hydro-pneumatic shock absorber consist-` ing of a cylinder; an internal metering rib on the wall of the cylinder; a hollow piston slidable in the cylinder, the head of said piston having a port atthe edge thereof for coaction with said metering rib to provide for a metered ow of liquid from beneath the piston head through the said port into an annular space defined between the hollow piston and the cylinder, and the wall `of said piston having a port to permit the flow of liquid from the annular chamber into the hollow piston; a floating piston interposed between the head of the hollow piston -and the lower end of the cylinder; and a compressed air chamber carried'by and in communication with the lower end of the cylinder.

7. In a hydro-pneumatic shock absorber, a cyl- 5 inder, a floating piston therein, an air chamber/A on one side of said floating piston controlled as to volume by the movements of said piston, and variable liquid metering means in the shock absorber on the opposite Vside of said floating piston, the floating piston being arranged to be moved for compressing air at the end of the liquid metering stroke.

8. In a hydro-pneumatic shock absorber, a cylinder, a floating piston therein, an air chamber l5 on one side of said floating piston controlled as to volume by the movements of said piston, a smaller cylinder slidable in said first named cyl-V I inder, and means for variably metering liquid by the relatively inward movements of .said two cylinders, said small cylinder being adapted and arranged at the end of its compression stroke to move said floating piston to compress the air in the air chamber.

9. In a hydro-pneumatic shock absorber, a cyl- 25 inder, a floating piston therein, means on one side of the floating piston for 'cushioning the movement of the latter, an incompressible fluent medium on the opposite side of the floating piston, a piston slidable in said cylinder for -move- 30 ment through said medium into and out of contact with the floating piston, and means providing for a metered flow of the medium from one side of the slidable piston to the other and functioning to progressively restrict the flow as the slidable piston approaches the fioating piston.

10.'In a hydro-pneumatic shock absorber, a cylinder, a floating piston therein, an air cushion on one side of the floating piston, an incompressible fluent medium on the opposite side of 40 the oating piston, a smaller cylinder slidable in the .first-mentioned cylinder for movement through the said incompressible fluent medium into and out of engagement with the floating piston, and means for variably metering the flow of the fluent medium past the smaller cylinder' upon the relative inward movements of the two cylinders so that upon heavy shock there will be more tendency for the floating piston to move before the smaller cylinder engages it than there will be when the shock is of less force, therebyobtaining the assistance of the air cushion earlier in the one case than in the other.

RANDOLPH P. WILLIAMS. 

